1. Technical Field
The present disclosure relates to methods for testing lithium ion batteries and evaluating safety of lithium ion batteries.
2. Description of Related Art
Safety is a concern in utilizing lithium ion batteries in electric vehicles (EV) and hybrid electric vehicles (HEV). Accidents are generally due to an internal short circuit which causes thermal runaway of the lithium ion battery. One reason for the internal short circuit of the lithium ion battery is over charging of the lithium ion battery, which results in the lithium ion battery being charged to a high voltage beyond the charging cut-off voltage. Therefore, evaluating the safety of the lithium ion battery, especially evaluating the over charging endurance ability of the cathode electrode, is very important.
In related art, methods for evaluating the safety of the lithium ion battery consists of evaluating the amount of heat generated during the over charging process, and the occurring time and temperature of the thermal runaway of the lithium ion battery. However, the temperature of the thermal runaway of the lithium ion battery is affected by many factors such as a battery structural design and an environmental temperature. Results may be different when testing the temperature is done on an outside surface of a battery shell, an inside surface of a battery shell, a top portion of a battery shell, or a connecting member of the battery. Different heat dissipation speeds caused by different surrounding temperatures can also affect the temperature testing result of the lithium ion battery. Thus, the temperature data of different sizes, different structural designs, or different batches of lithium ion batteries cannot be compared. Therefore, the evaluation and investigation of the safety of the lithium ion battery may be difficult and inaccurate by testing the temperature of the lithium ion battery. The temperature data cannot truly reflect the over charging endurance ability of a cathode electrode of the lithium ion battery.
What is needed, therefore, is to provide a method for testing the lithium ion battery and a method for evaluating the safety of the lithium ion battery not affected by battery structural designs and environmental conditions, accurately reflect the over charging endurance ability, and accurately evaluate the safety of the lithium ion battery.